A Phase 1 Dose Escalation Study of Infusion of Ex Vivo CD3/CD28 Costimulated Umbilical Cord Blood-Derived T Cells in Adults Undergoing Transplantation for Advanced Hematologic Malignancies

Abstract 3032

Successful outcomes following umbilical cord blood transplantation (UCBT) are limited in large part by delayed engraftment, impaired immune reconstitution and an inability to give donor lymphocyte infusions (DLI) in the event of relapse or graft failure. Recent studies suggest double UCBT enhances hematopoietic recovery and may improve leukemia free survival, despite the engraftment of only one unit. Our previous work in a preclinical (xenograft) model showed that T cell activation can enhance hematopoietic recovery after single UCBT. Thus we performed a phase 1 study testing safety and defining the maximum tolerated dose (MTD) of ex vivo CD3/CD28 costimulated UCB-derived T cells co-infused with single UCB grafts in patients with advanced hematologic malignancies. A second objective was to test the feasibility of ex vivo expansion and cryopreservation of UCB T cells for administration as DLI in the event of disease relapse. Eligible subjects had no suitable related or unrelated donor, and had a single 4/6 (or better) HLA-matched UCB graft containing at least 2.5 × 10⁷ nucleated cells/kg. Single umbilical cord blood units stored in 2 fractions were eligible for the intervention. The smaller fraction was thawed 10–14 days prior to infusion and cultured with magnetic beads conjugated to antibodies directed against CD3 and CD28. After myeloablative conditioning, the larger unmanipulated UCB fraction was infused, followed immediately by a fixed dose of the expanded CD3/CD28 costimulated T cells. The remainder of the costimulated T cells were cryopreserved for potential future use as DLI. Four dose levels of initial costimulated T cells (10⁵-10⁸ T cells/kg) were planned. 5 subjects enrolled on the trial; 4 underwent UCBT all of whom were treated at the first dose level (10⁵cells/kg). There were no infusion related adverse events; the dose limiting toxicity (DLT) was conservative and defined as grade 3 or grade 4 GVHD within the first 90 days following UCBT. An MTD was reached at the 10⁵ cells/kg dose level with two subjects experiencing grade 3 GVHD of the gut on days +40 and +27 respectively. For the first 3 subjects enrolled on study, neutrophil engraftment occurred on days +20, +12, and +17, while the fourth subject experienced primary graft failure and received a second mismatched unrelated donor graft. One subject experienced platelet engraftment on day +23. Early (day +11) donor T cell trafficking was documented in this subject's skin using fluorescence in situ hybridization directed at the Y chromosome, and one year post-transplant bone marrow morphologic findings were notable for an exuberant expansion (20% of cellularity) of physiologic precursor B lymphoblasts (hematogones) with a maturing B cell phenotype which correlated with CD4+ immune reconstitution in peripheral blood. Cytokines were measured in the supernatants from expanded T cells and in serum from all subjects. Supernatants contained supraphysiologic levels of cytokines important for engraftment/progenitor/dendritic cell development (GM-CSF, IL-3, FLT-3L) as well as T and B cell differentiation/function (IL-2, IL-4, IL-10, IFN- γ, BAFF). Serum cytokine measurements in recipients were notable for measurable increases in IL-10 following the infusion of expanded T cells for all subjects, with absolute levels lower in the two subjects with DLTs. 3 of 4 expansions yielded adequate numbers of cells for cryopreservation as future use for DLI. Taken together, these preliminary data are consistent with our preclinical observations of rapid engraftment in recipients of a single UCBT combined with relatively low doses of activated T cells. Additional safety studies are needed to determine the optimal T cell dose. If confirmed in larger numbers of patients, this represents an attractive strategy for improving engraftment, immune reconstitution, as well as a method to enable DLI following UCBT.